Cast iron



Patented Apr. 6, 1937 UNITED STATE S PATENT OFFICE No Drawing. Application April 16, 1935, Serial- No. 16,718. In Great Britain October 24, 1934 1 Claim.

Cast iron in order to be -fiuid enough to flow easily into moulds always contains carbon, sulphur phosphorus and silicon, and on account of the last three ingredients is noted for its brittleness, and unless high in silicon (which increases the brittleness) is not resistant to corrosion. It is also very liable to cracking with sudden changes of temperature. This invention relates to an improved manufacture of cast iron which is very in fluid when molten, highly resistant to corrosion and is unafiected by sudden changes of temperature up to 1,500 F. and although extremely hard when cast is not brittle, and the carbon can be changed in structure by heat treatment.

According to this invention to of ferrochrome carbide to chromium,

4% to 10% carbon, remainder iron) is alloyed with 60% to of iron in which the sulphur I phosphorus and silicon are low (wrought iron, or

. iron prepared by converter or open hearth processes, or triplex 'converterelectric process-are suitable, although iron direct from the cupola can be used for castings only) and not more than 5% of copper and 5% of molybdenum, so that extremely hard castings highly resistant to corrosion can be produced at once (without riitriding) which are not brittle but suitable to withstand hard wear, abrasion and concussion due to impact (such as road marking, studs, paving, linings 30 of guns and engine cylinders).

The hardness varies with the carbon content, which is from 2% to 9% when cast (the maximum carbon of ordinary cast iron is about 4%).

Aluminum, manganese or titanium can be used as usual for de-oxidizing.

If extreme toughness is required combined with ability to withstand shock (penetration by bullets or projectiles) large proportions of manganese (up to 15%) can be added in which case for 40 machining properties lead can be added in suitable proportions not exceeding 20% 0! the chromium content with which it alloys and counteracts the hardness, the copper facilitating.

Malleabllity and ductility can be obtained by lightly hot working above l,500 F. as under these conditions the ferrochrome carbides in the presence of copper and molybdenum apparently change their crystalline condition (which gives extreme hardness) to a colloidal form (permitting working) by means of the copper-molybdenum and colloidal carbon entering into solution with the iron andchanging the structure. Iron that can be hot worked is usually practically carbon free, it containing rarely more than 5% carbon. As an example of carrying this invention into effect, I take 30% ferrochrome carbide, 2% copper, lead, molybdenum, 1% manganese oxide, 66% iron, and this mixture will produce a cast iron extremely hard when cast which fills moulds perfectly, being if lightly worked (hammered) and brought to a yellow heat, changes its fine crystalline mixture to a fibrous one, and can be forged like ordinary iron without extensive heat treatment, the carbon still being present but changed in quality, now being in a colloidal condition. By this invention, manganese alloys which are extremely hard and tough but diiiicult if not impossible to machine, can be'made easily machinable by supplementing a 10% to 15% portion of the iron by manganese, and increasing the lead to 2%.

What I do claim as my invention and desire to secure by Letters Patent is:-- I

An alloy containing 2 to 9% carbon, 15 to 24% chromium, up to 5% molybdenum and copper, 10 to 15% manganese, 2% lead, with the balance iron plus impurities.

THOMAS DANIEL KELLY. 

